package l.l.w.tengxun._01;

import sun.misc.resources.Messages_sv;

import java.math.BigInteger;
import java.util.Scanner;

/**
 * Created by llw on 2018/4/5/0005.
 */
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNextInt()) {//注意while处理多个case
            int n = in.nextInt();
            int m = in.nextInt();
            String n_str = Integer.toString(n, 10);
            BigInteger n_big = new BigInteger(n_str);
            String m_str = Integer.toString(m, 10);
            BigInteger m_big = new BigInteger(m_str);
            Integer integer = new Integer(2);
            BigInteger result = n_big.divide(new BigInteger(integer.toString())).multiply(m_big);
            System.out.println(result.toString());
        }
    }
}
